layout.public.php is broken

[nickvergessen]

Not sure where that file is used, but it spams our sentry instance with quite some log messages:

• Undefined index: header-classes:
  https://github.com/nextcloud/server/blame/84c46dd3dd9a9b20d066ea704593a96ff0db0523/core/templates/layout.public.php#L33
• Undefined index: user_displayname
  https://github.com/nextcloud/server/blame/84c46dd3dd9a9b20d066ea704593a96ff0db0523/core/templates/layout.public.php#L3
• "Undefined variable: template" see next for details
• Call to a member function getHeaderTitle() on null
  https://github.com/nextcloud/server/blame/84c46dd3dd9a9b20d066ea704593a96ff0db0523/core/templates/layout.public.php#L38

@juliushaertl @danxuliu @skjnldsv as authors of the file. Which page is using this?

[nextcloud-bot]

GitMate.io thinks possibly related issues are #10442 (Contact list broken layout), #4837 (Layout of error page broken), #6622 (Settings menu layout is broken), #6784 (Php error?), and #10241 (php segmentation fault on /public.php/webdav/).

[juliusknorr]

From the sentry log it seems that some public pages like the calendar use 'public' as $renderAs parameter in the TemplateResponse constructor, which leads to loading the layout.public.php file. That should instead only happen if a PublicTemplateResponse is used. I'll look into it.